ping: tests: Cleanup IPOption()s

Scapy now only accepts known options with IPOption(), so our unknown
option must be passed raw.

While here, prefer the named options for EOL and NOP.

Reviewed by: emaste, kp
Approved by: emaste (mentor)
Differential Revision: https://reviews.freebsd.org/D47160

(cherry picked from commit 2e29bf7a2ae66acb6e65ffc1c923cfb373af67bd)